The present invention relates to a method and system for dispensing a compressed gas into a receiving vessel, and more specifically to a method and system for dispensing a compressed gas as in particular hydrogen into a receiving vessel, such as a vehicle fuel tank, rapidly but nevertheless safely.
When dispensing a compressed gas into a receiving vessel, care has to be taken that the receiving vessel does not overheat. Overheating may occur as a result of adiabatic compression of the gas. If the gas is hydrogen or helium, the reverse Joule-Thompson effect will also contribute in heating the vessel. Gas filling protocols, in particular hydrogen fueling protocols, that are most commonly in use are based on worst case assumptions when selecting appropriate filling rates. Since receiving vessels seldom have worst case properties, and vessel conditions are seldom worst case conditions, and therefore the commonly used protocols are often excessively conservative and result in prolonged time for dispensing the compressed gas.
U.S. Pat. No. 6,619,336 (Cohen et al.) improves the dispensing operation in that the pressure and temperature are determined and the density of the gas in the receiving vessel is calculated therefrom. This actual density is compared with a vessel-rated density to control the flow of the compressed gas in response to the comparison. If the actual density in the receiving vessel is greater than or equal to the rated density, minus a tolerance, gas flow is halted, and either resumed, if the actual density should have fallen below the rated density within a predetermined time interval, or terminated.
U.S. Pat. No. 7,178,565 (Eichelberger et al.) incorporates the ambient temperature to mitigate overheating the receiving vessel. Depending on the ambient temperature one of several predetermined rates of pressure rise, i.e. a pressure ramp rate, in the receiving vessel is selected. Furthermore, a temperature indicative for the temperature of the gas in the receiving vessel is measured during filling. The ramp rate is maintained at the selected value until the measured temperature reaches a preset upper limit. Upon reaching this temperature limit, an electronic controller commands a pressure control valve to temporarily pause at the instantaneous pressure level. The pause remains in effect until the instantaneous temperature at the receiving vessel has dropped to a predetermined value below the set temperature, at which time the pressure ramp rate is increased to its former high dispensing rate.
Start/stop methods, however, confuse the customer each time the dispensing process stops and restarts.
US 2007/0079892 A1 (Cohen et al.) discloses controlling the flow rate of the compressed gas by means of a pipe organ style flow control device composed of a plurality of fluid conveyance lines in parallel with each other and having differing orifice coefficients for transmitting gas at different flow rates therethrough. Each of the fluid conveyance lines can be opened and closed by means of a respective control valve commanded by a programmable flow controller including a desired ramp rate. A pressure monitor downstream of the fluid conveyance lines measures the pressure of gas being directed into the receiving vessel. The flow controller compares the desired pressure ramp rate with the measured pressure and controls the flow rate of gas through the fluid conveyance lines in response to the comparison. Monitoring temperature is not disclosed.
It is an object of the present invention to provide a method and system for dispensing a gas into a receiving vessel in a safe and time efficient manner.
It is desirable to dispense gas into the receiving vessel as quickly as possible, without violating the vessel temperature limit, which typically is 85° C. for vehicle fuel tanks.
A further object is to smooth out the dispensing process, i.e. to dispense gas into the receiving vessel at a dispensing rate which is steadier than with the conventional methods and systems, so that the customer experiences consistent flow rates and sounds during the dispensing process.
There is also a need for a method and system for dispensing a compressed gas, in particular hydrogen, into the fuel tank of a combustion engine or fuel cell vehicle in a time efficient manner without overheating the fuel tank.